S/S Mongoose Pup (Gnaw, Survival, Dive) is my go-to counter for Death Adder Hatchlings in PvP. With its 357 speed, it'll outpace the Adder which means Blinding Poison will only affect it for one round instead of the usual two. Combo that into Dive, a 2-turn move, and watch the Adder pop. The Pup can also serve as a soft counter to Val'kyrs due to being an aquatic. And then you have Survival, which can provide two extra turns if timed well. All-in-all, a great anti-meta pet.